1. Field of the Invention
The invention relates to a new pull-tab seal intended to seal a container with a plug or cap closure and the production method thereof.
2. Description of Related Art
Containers with a plug or cap closure are made leak-tight, before they are first opened, by means of a seal which may be bonded or sealed, particularly heat-sealed, on the mouth of the container.
The invention relates more specifically to a heat-sealable seal. Such a seal comprises an inner seal set in place over the entire periphery of the upper edge of the neck of the container or mouth, thereby isolating the container from the outside, and on the other hand, a generally thicker support, inserted into, but without being bonded to, the bottom of the plug. Prior to the first opening of the container, the support and the inner seal may be bonded by means of a temporary adhesive.
The function of the inner seal is first of all to make the container tamper-proof prior to the first opening. Additionally, it provides primary leak tightness with regards to the outside. Moreover, it has to develop certain compatibility properties with the contents that it is supposed to isolate and for example be of food grade quality if the recipient contains food.
The support, for its part, is intended to absorb the tolerances between the bottom of the cap and/or plug and the upper part of the neck of the container, and additionally, to provide secondary leak-tightness if the inner seal has been fully or partly removed. It is therefore able to provide a certain memory-effect compression precisely so as to absorb these tolerances.
In practice, the seal is inserted inside the cap or plug. Once the container is filled, the plug or cap fitted with the seal is screwed or snapped onto the container. The inner seal part of the seal is then in contact with the mouth of the container. The inner seal is then sealed on the mouth of the container by heat-sealing induction. Said heat-sealing is made possible by the combined action of a layer of conductive material inserted in the seal, which heats up under the effect of electrical induction, causing the sealing film to soften and to bond to the mouth. The conductive material is inserted in the thickness of the inner seal. When the container is opened for the first time, the support inserted inside the plug separates from the inner seal which remains sealed onto the mouth. It is only afterwards that the inner seal is removed by the consumer, the leak-tightness, in the closed position of the container, then being only provided by the compression of support of the seal on the mouth.
In order to provide an inner seal that can be effectively and easily torn off by the consumer, an easy-grasp pull-tab has been added to said inner seal, as described for example in document FR-A-2 716 407.
Nonetheless, the presence of this protuberant pull-tab makes it difficult to place the seal inside the plug or cap, because of the resulting over-thickness along the edge of the seal. It is furthermore difficult to place the pull-tab safely relative to the thread or to the clips arranged in the plug or cap so as to prevent any risk of damage to the pull-tab at the time of closing or opening the plug or cap.
Prior art document DE3920324 describes an induction heat-sealable seal comprising a support and an inner seal fitted with a pull-tab, the support and the inner seal being at no time bonded to one another. Of three embodiments shown, only one of them (FIG. 1) comprises a pull-tab folded back over its entire surface. Said pull-tab is formed by associating a membrane and a heat sealable layer, the aluminum foil being in the support.
Document JP 2000-191021 describes a seal made up of a support and an inner seal joined by means of a temporary adhesive. The seal contains a pull-tab which is either folded back over the support or hangs along the mouth.
Document U.S. Pat. No. 4,754,890 describes an inner seal and a support which are never joined by means of a temporary adhesive.
Document GB 2 330 134 describes a seal wherein the support and an inner seal are bonded by means of a wax layer. This seal has a pull-tab which is folded back, with the heat-sealing layer of the pull-tab being between the support and the inner seal.
Prior art document EP 2 045 194 A1 describes a seal that comprises a support and an inner seal fitted with a pull-tab. Support and inner seal are bonded by means of a temporary adhesive applied to the inner seal, after the pull-tab has been folded back. In a first embodiment, the pull-tab solely comprises a reinforcing layer with no heat-sealing layer. In this case, delamination of the layers constituting the inner seal may occur when the seal is peeled off. In a second embodiment, the pull-tab comprises an aluminum layer and exhibits an S-shape when it is folded back. The presence of these two folds definitely increases the thickness of the pull-tab which makes temporary assembly of the inner seal and the support quite difficult.
Document WO 2010/115811 describes a seal of the same type as above. When the pull-tab contains an aluminum layer, it systematically comprises a heat-sealing layer on its lower surface. To prevent the bonding of the sealing layer to the lower surface of the support at the moment of induction, the heat-sealing layer is advantageously coated with an anti-adhesive film. Such an embodiment increases the number of layers and the cost of production. At the same time, in the preferred embodiment, the pull-tab comprises a reinforcing layer adjacent to the sealing layer, said pull-tab being devoid of a heat-sealing layer and folded back over an aluminum foil.
Even if the seals proposed in the prior art provide some worthwhile solutions, there are still a number of problems to be resolved and in particular:                the layers constituting the inner seal may delaminate upon peeling off said inner seal when the pull-tab is not formed in the entire thickness of the inner seal, the mechanical strength of the pull-tab may be more or less strong depending on the nature and number of layers constituting the inner seal,        when the pull-tab is provided with heat-sealing film, the pull-tab may bond to the support at the time of induction,        when the sheet of a conductive material is included in the pull-tab, the seal under the pull-tab at the moment of induction may be too weak, making it necessary to increase the induction power and therefore to reduce the possible induction temperature range when sealing, and        the rigidity of the inner seal with respect to its thickness, which is generally greater than 200 micrometers, the manufacturing method which still requires a relatively high number of steps that also affect the production cost.        